India's vanishing groundwater
Two new studies suggest that India's aquifers are undergoing rapid depletion due, almost entirely, to water withdrawals for agricultural use. Satellite measurements indicate that the water table is sinking faster than anyone had previously estimated, with potentially dire implications for the 600 million people living regionally — nearly one-tenth of humanity — who rely on it.Skip to next paragraph
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From the Nature study press release:
Using satellite data, UC Irvine and NASA hydrologists have found that groundwater beneath northern India has been receding by as much as 1 foot per year over the past decade – and they believe human consumption is almost entirely to blame. More than 109 cubic kilometers (26 cubic miles) of groundwater disappeared from the region's aquifers between 2002 and 2008 – double the capacity of India's largest surface-water reservoir, the Upper Wainganga, and triple that of Lake Mead, the largest manmade reservoir in the U.S.
Surface water percolating down from rain, snow, lakes, and rivers recharges aquifers. Some aquifers contain water that's thousands to millions of years old. (According to New Scientist, the world's oldest aquifer lies beneath the Sahara — rain that fell perhaps 1 million years ago.)
How does this bode for India's agriculture? NASA's Matt Rodell, lead author on the Nature study, says: "If measures are not soon taken to ensure sustainable groundwater usage, consequences for the 114 million residents of the region may include a collapse of agricultural output, severe shortages of potable water, conflict, and suffering."
During the second half of the 20th century, water withdrawals increased dramatically. Beginning in the 1960s — the Green Revolution — the Indian government instituted policies meant to boost agricultural production. As a result, the amount of irrigated land in India nearly tripled between 1970 and 1999. In northern India, agriculture is responsible for up to 95 percent of groundwater use.
Science News says of the study reported in Geophysical Research Letters:
In the mid-1990s, India’s Central Ground Water Board estimated that farmers pulled more than 172 cubic kilometers of water each year from aquifers in the study region of northeastern India, southern Nepal and western Bangladesh.... That’s more than three times the volume of India’s largest surface reservoir. New data gleaned from gravity-measuring satellites suggest that the annual rate of extraction in that region has jumped more than 60 percent since then.